In frequency standards that rely on alkali metal source atoms, such as atoms of cesium 133 or rubidium 85 or 87, a modulatable light source, such as a laser light source, is used to optically pump the source atoms contained in a cell of the frequency standard. A sealed, optically transparent cell contains the source atoms and any buffer gases, and the RF modulated light from the light source is directed through suitable optics into the cell. When the source atoms within the cell absorb light of a particular wavelength that is modulated at a particular modulation frequency, they emit a light signal whose intensity has a sharply defined peak at this wavelength. This light signal is detected as an output of the frequency standard.
This detected light may then be used to control the frequency of the light source emission so that the intensity of the light output from the source atoms is maintained at this peak. Because the peak intensity is very sharply defined, the modulation frequency can then be used to very accurately drive a clock.
Present atomic frequency standards have sizes averaging in the vicinity of 3 inches by 3 inches by 6 inches. Efforts have been made to reduce this size particularly for applications in the fields of telecommunications, satellite navigation transmitters and receivers, and the like.
Once such effort has been directed to a design involving a frame element on which an optical physics package and an electronic control and detection package are mounted. The optical physics package includes a solid state laser source, a linear polarizer, a circular polarizer, a sealed and windowed metallic cell containing the source and buffer gas atoms, and a photodetector. The electronic control and detection package cooperates with the physics package to control and modulate the laser source and to detect the light output. This package is reported to have a size of 1.5 inches by 1.5 inches by 2.5 inches.
The present invention achieves even smaller dimensions by employing MicroElectroMechanical Systems (MEMS) technology in fabricating both the optics and the detection components on the same substrate. The size of the MEMS frequency standard according to the present invention may be on the order of 1.5 mm deep by 1.5 mm high by 2.0 mm long.